error 8002009 - type mismatch

Here's my code....

                     dim oWebi
      dim objXML
      dim rs
      
      set oWebi = server.CreateObject("Webi.bWebi")
      set rs = oWebi.AddNewRegistrant
      set objXML = server.CreateObject("MSXML.DOMDocument")
      objXML.async = false
      objXML.load request
      rs.fields("webi_id") = clng(Request.QueryString("id"))
      rs.fields("first_name") = objXML.selectSingleNode("//first_name").text
      rs.fields("last_name") = objXML.selectSingleNode("//last_name").text
      rs.fields("email") = objXML.selectSingleNode("//email").text
      rs.update
      oWebi.SaveRegistrant(rs)
      Response.Write true      

It was working...  I get an mismatch error 8002009  on this line oWebi.SaveRegistrant(rs)